© 2017. Published by The Company of Biologists Ltd | Disease Models & Mechanisms (2017) 10, 691-704 doi:10.1242/dmm.029009 REVIEW SPECIAL COLLECTION: NEURODEGENERATION Induced pluripotent stem cell models of lysosomal storage disorders Daniel K. Borger, Benjamin McMahon, Tamanna Roshan Lal, Jenny Serra-Vinardell, Elma Aflaki and Ellen Sidransky* ABSTRACT lethal acute neuronopathic disease. Even within a given LSD, there Induced pluripotent stem cells (iPSCs) have provided new can be vast phenotypic heterogeneity, with many LSDs exhibiting opportunities to explore the cell biology and pathophysiology of both early- and late-onset forms (Boustany, 2013). human diseases, and the lysosomal storage disorder research Individual LSDs are extremely rare disorders, but taken together, community has been quick to adopt this technology. Patient-derived they are thought to affect up to 1 in 4000 live births (Al-Jasmi et al., iPSC models have been generated for a number of lysosomal 2013; Applegarth et al., 2000; Meikle et al., 1999; Pinto et al., 2004; ̌ storage disorders, including Gaucher disease, Pompe disease, Fabry Poorthuis et al., 1999; Poupetová et al., 2010). Furthermore, due in disease, metachromatic leukodystrophy, the neuronal ceroid part to the multi-organ nature of many of these diseases, and lipofuscinoses, Niemann-Pick types A and C1, and several of the because of a continuing lack of truly effective treatments for many mucopolysaccharidoses. Here, we review the strategies employed for LSDs, these diseases are often characterized by high mortality reprogramming and differentiation, as well as insights into disease and morbidity (Stone and Sidransky, 1999). Current therapies are etiology gleaned from the currently available models. Examples are extremely costly and are often lifelong treatments. LSDs therefore provided to illustrate how iPSC-derived models can be employed to constitute a significant burden on affected individuals and their develop new therapeutic strategies for these disorders. We also families and on healthcare systems as a whole, and LSDs have long discuss how models of these rare diseases could contribute to an been a major focus of rare disease research. Moreover, a growing enhanced understanding of more common neurodegenerative appreciation of the role of lysosomal dysfunction in aging and age- disorders such as Parkinson’s disease, and discuss key challenges related neurodegenerative disorders has led to a recent surge of and opportunities in this area of research. interest in LSDs. These factors have combined to help fuel the application of a number of emerging biotechnologies towards LSD KEY WORDS: Gaucher disease, IPSC models, Lysosomal enzymes, research. However, there has been mixed success in generating Lysosomal storage disorders, Neurodegeneration suitable animal models of LSDs for research in this field (Farfel- Becker et al., 2011; Lawson and Martin, 2016; Pastores et al., 2013), Introduction and hence investigators have directed efforts toward developing There are over 50 types of lysosomal storage disease, a class of alternative disease models. inherited metabolic disease caused by the absence or deficiency of a One technology in particular – the development of induced lysosomal protein. Most lysosomal storage diseases (LSDs) result pluripotent stem cells (iPSCs) – has been broadly adapted by from mutations in metabolic enzymes that are active in the investigators researching the LSDs, and human iPSC lines are already lysosome, although a handful are caused by defects in lysosomal contributing significantly to our understanding and treatment of these transport or vesicular trafficking (Boustany, 2013; Feng et al., 2002; rare diseases. Here, we review the use of human iPSCs in LSD Ward et al., 2000). Regardless of the function of the mutated gene, research, highlighting the strategies that have been used to generate LSDs are universally characterized by the intracellular accumulation iPSCs and iPSC-derived cell models and to evaluate their relative of undigested storage material, although the composition of this success in accurately phenocopying the human disease. The benefits material varies between the LSDs. The deficiency of functional of these cells in untangling disease etiology and developing novel protein and the subsequent accumulation of storage material can therapeutics are discussed, as well as the limitations. We also briefly impair normal lysosomal function in affected cells and interrupt a highlight how the insights gleaned from studying LSDs using these diverse array of cellular activities (Ballabio and Gieselmann, 2009). cellular models could contribute to a better understanding of more The phenotypic consequences in patients are extremely varied, common neurodegenerative diseases. ranging from asymptomatic or sub-clinical manifestations; to chronic visceral, musculoskeletal or immunological disease, to Induced pluripotent stem cells: an overview In 2006, Shinya Yamanaka and his colleagues at Kyoto University reported that by forcing expression of four genes – OCT3/4, SOX2, Medical Genetics Branch, National Human Genome Research Institute, National KLF4 and MYC (collectively known as OSKM) – via retroviral Institutes of Health, Bethesda, MD 20892, USA. transduction, they were able to convert murine fibroblasts into fully *Author for correspondence ([email protected]) pluripotent stem cells. The profile and potency of these murine iPSCs were similar to those in embryonic stem cells (Takahashi E.S., 0000-0002-3019-8500 and Yamanaka, 2006). The following year, three papers – one by This is an Open Access article distributed under the terms of the Creative Commons Attribution Yamanaka’s group (Takahashi et al., 2007) and one by George License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, ’ distribution and reproduction in any medium provided that the original work is properly attributed. Daley s group (Park et al., 2008a), both using the OSKM cocktail, and a third by James Thomson’s group (Yu et al., 2007) using Received 27 December 2016; Accepted 28 April 2017 OCT3/4, SOX2, NANOG and LIN28 (OSNL) – showed that the Disease Models & Mechanisms 691 REVIEW Disease Models & Mechanisms (2017) 10, 691-704 doi:10.1242/dmm.029009 same basic technique used in mice could also be employed to neuronopathic (type 1), acute lethal neuronopathic (type 2), and generate iPSCs from human somatic cells. Since then, numerous chronic neuronopathic (type 3), and more severe mutations are advances have been made in identifying new factors that induce associated with neuronopathic manifestations. Furthermore, reprogramming, which now include RNAs and small molecules, population studies have established that individuals with GBA1 new modes of introducing the necessary factors to cells, and new mutations, both carriers and affected individuals, are at an cell types that can be reprogrammed (Table 1). These discoveries increased risk of developing Parkinson’s disease, an age-related have done much to inform our understanding of how stem cells neurodegenerative disorder, as well as other Lewy body disorders achieve and maintain pluripotency. Recent work clearly (Nalls et al., 2013; Sidransky et al., 2009). The discovery of this link demonstrates how iPSC-derived cells are a remarkable tool for between GBA1 and Parkinson’s disease has played a large part in a research of human diseases (see Box 1). These advantages have recent explosion of GD research. made iPSC-derived cell models a natural choice for studies of the However, both seasoned GD researchers and those new to the LSDs, as discussed below. field have been limited by a dearth of effective models for studying both GD and GBA1-associated Parkinson’s disease. Mouse models iPSC models of LSDs for GD have been developed, but none faithfully recapitulate the Cells of the neuronal and hematopoietic lineages are the usual features of the disease seen in humans (Farfel-Becker et al., 2011) differentiation targets for iPSC-derived models of LSDs (28 of 39 Human cell lines have also been of limited use. Fibroblasts from studies pursuing differentiation; see Table 2) because these are the patients with GD have long been used to study the disease, but these cells most often affected by these diseases (Figs 1 and 2). Although cells do not store the implicated glycolipids and do not show murine iPSC lines have been derived from five mouse models of obvious signs of pathology (Saito and Rosenberg, 1985). Applying LSDs (Kawagoe et al., 2011; Meng et al., 2010; Ogawa et al., 2013), conduritol β-epoxide (CBE), an irreversible inhibitor of human iPSCs and iPSC-derived cell models, which have been glucocerebrosidase, to a common human monocytic cell line such generated for at least 11 LSDs (Table 2), have become the focus of as THP-1 or to SH-SY5Y cells (a human neuroblastoma cell line the field, as they more closely mimic the human disease. As used to model neurons) leads to glycolipid accumulation in these discussed below, human iPSC models of LSDs are already cell lines, and this approach has been used to provide in vitro models contributing to our understanding and treatment of these rare for GD (Hein et al., 2007; Prence et al., 1996). However, it is diseases. difficult to generalize findings in immortalized cell lines to cells in vivo. The limited options for studying GD in the laboratory has Gaucher disease directed attention toward iPSCs. Gaucher disease (GD) is a recessive disorder caused by mutations in As macrophages